1. Field of the Invention
The invention relates to a trajectory tracking control system and method for a mobile unit, and in particular to a system and method for controlling trajectory tracking of a robot.
2. Description of the Related Art
A technology has been proposed, which controls a mobile unit, such as a vehicle and a robot, to track a target path automatically. For example, there is a technology that performs automatic trajectory tracking of a mobile unit by performing feed-back control on the amount by which the position of the mobile unit deviates in the lateral direction and the amount of deviation of azimuth angle of the mobile unit. However, when only such feed-back control is performed, the response of the mobile unit to changes in the curvature may be delayed, and therefore it is difficult for the mobile unit to track a target path including curves having various curvatures.
To solve this problem, JP-A-2002-215239 proposes a technology in which the steering angle of a mobile unit is determined based on the operation amount that is set by feed-forward control on the curvatures of a target path and the positional deviation of the mobile unit in the lateral direction, as well as the operation amount that is set by feed-back control on the positional deviation of the mobile unit in the lateral direction and the deviation of azimuth angle relative to the target path. According to this technology, the mobile unit can accurately track a target path having various curvatures.
However, according to the tracking control technology described in JP-A-20020215239, the curvature of the target path is directly put into the control loop, and therefore the behavior of the mobile unit directly reflects discontinuous changes in the curvature of the target path, and as a result, the motion of the mobile unit becomes unstable. In addition, because the mobile unit is always subjected to the free-forward control, when the mobile unit largely deviates from the target path, the operation amounts provided by the feed-forward control act as disturbances to the operation amounts provided by the feed-back control, and as a result, the accuracy of the trajectory tracking deteriorates.